1. Field of the Invention
The present invention relates to a semiconductor module, and more particularly, to a semiconductor module comprising a plurality of semiconductor chips mounted on a single substrate.
2. Description of the Background Art
FIG. 7 is a conceptual drawing showing a first example configuration of a conventional semiconductor module. A conventional semiconductor module 10 comprises a plurality of semiconductor chips 12 mounted on a single substrate. Each of the semiconductor chips 12 comprises a core circuit 14, such as a memory cell array or a like circuit, and a plurality of input/output pins 16. In FIG. 7, the plurality of input/output pins 16 are simply denoted by a single line.
The input/output pins 16 of the semiconductor chip 12 are connected to input/output pins 20 of the semiconductor module 10 by way of a level conversion element 18. In FIG. 7, the plurality of input/output pins 20 are simply denoted by a single line. The level conversion element 18 is an interface for establishing a match in signal voltage between a circuit disposed outside the semiconductor module 10 and the semiconductor chip 12. An address signal and a data signal are exchanged between the input/output pins 20 and an external circuit.
The semiconductor module 10 is shipped after being subjected to diagnosis as to whether or not the module operates properly. The diagnosis mentioned above is significantly more complex and time consuming than a diagnosis performed on a single semiconductor chip 12. Development of a program for performing such a diagnosis involves an enormous cost and a great deal of time. Moreover, specifying a defective semiconductor chip on the basis of the diagnosis is not necessarily easy.
FIG. 8 is a conceptual drawing showing a second example configuration of a conventional semiconductor module. In FIG. 8, those elements, which are the same as the constituent elements shown in FIG. 7, are assigned the same reference numerals, and repetition of their explanations is omitted. In a semiconductor module 30 shown in FIG. 8, each of a plurality of semiconductor chips 32 has a diagnostic circuit 34. Upon receipt of a predetermined signal from an external circuit, the diagnostic circuit 34 tests the status of the semiconductor chip 32 and outputs the result to the external circuit. In a case where the semiconductor module 30 is a target of the test, the diagnostic circuit 34 can readily detect whether an individual semiconductor chip 14 is non-defective or defective. Accordingly, the configuration shown in FIG. 8 can eliminate difficulty that would otherwise be encountered in specifying a defective chip.
In a case where the semiconductor chips 32 shown in FIG. 8 are target of the test, the plurality of diagnostic circuits 34 provided for the respective semiconductor chips 32 must be controlled individually. In such a case, it becomes necessary that the external circuit individually reads the diagnostic results output from the respective diagnostic circuits 34. Even in a case where the diagnostic circuit 34 is housed in the semiconductor chip 32, diagnosing the semiconductor module 30 requires a complicated control program and a great deal of diagnostic time.
If the semiconductor module 10 or 30 is found to incorporate a defective chip, replacement of the chip is not easy. For this reason, if the semiconductor module 10 or 30 incorporates even a single defective chip, the module 10 or 30 as a whole is diagnosed as being defective. As mentioned above, since comprehensive diagnosis of a conventional semiconductor module is not easy and replacement of a defective chip is not easy, there arises a problem of an increase in manufacturing cost and the number of manufacturing steps.
The present invention has been conceived to solve the above-described problem and is aimed at providing a semiconductor module in which the entirety of a plurality of semiconductor chips can be diagnosed readily.
The present invention is also aimed at providing a semiconductor module in which a defective chip can be readily replaced.
The above objects of the present invention are achieved by a semiconductor module including a plurality of semiconductor chips to be mounted on a single substrate. The semiconductor module includes a mode signal pin for receiving a mode signal for requesting performance of a diagnostic operation the semiconductor module also includes a result output pin for outputting a result of diagnosis. The semiconductor module further includes diagnostic circuits for diagnosing the statuses of the corresponding semiconductor chips. The diagnostic circuits are controlled by a diagnosis controller such that all the semiconductor chips are diagnosed in parallel or serially after a mode signal for requesting a diagnostic operation has been supplied to the mode signal pin.